Nautical fictions and other adventure stories are often filled with horrifying instances of ships being stranded at sea- due to storms and technical failures- not knowing the right direction. It’s true that, unlike on land, navigation in the open ocean is significantly difficult.
The sea, with its vastness and unpredictable chaos within, always offer an uncertain journey for the captain and other sailors. For navigators, while the land offers a number of fixed visible cues in the landscape, the sea does not leave any useful, distinguishing features.
Due to this complexity, marine navigation has evolved significantly since the origin of humankind, finding various methods and measurements to save the life of mariners.
For many, the first encounter with the measurements being followed at sea raises eyebrows, wondering why they need to be different from miles and kilometres used while talking about land. Unlike measuring distance and speed on land, sailors use nautical mile as well as a knot for measurements during the sail.
At sea, in navigational calculations, the statute mile is considered an arbitrary length of no particular significance. And, in particular, the replacement of the ordinary measurement with nautical miles and knots at sea helps the Mariners to quickly read charts that use latitude and longitude.
Currently, the nautical mile is used as the unit of measurement by all countries for air and sea navigation.
What is Nautical Mile?
- A nautical mile, a unit of measurement defined as 1,852 meters or 1.852 kilometres, is based on the circumference of the earth and is equal to one minute of latitude.
- If one is to pick a part of the earth after cutting the planet in half at the equator and consider the equator as a circle, it can be divided into 360 degrees.
- Then, one degree can be split into 60 minutes, of which one minute of arc on the planet Earth is 1 nautical mile. One nautical mile is slightly more than a statute mile (1 nautical mile = 1.1508 statute miles).
- According to the English measurement system, a nautical mile is equal to 1.1508 miles, or 6,076 feet.
What is Knot?
- Then comes the knot. Of course, here we are not talking about sailing knots, such as Figure-8 Knot. The knot here, the nautical knot, is a unit of speed equal to one nautical mile per hour (1 knot = 1.15 miles per hour) or approximately 1.15078 mph.
- Similar to the speed and distance measurement on land, the nautical mile and knot explain the movement of a vessel at sea. For instance, a boat or ship travelling at 15 knots could go 15 nautical miles per hour.
History of Maritime Navigation
Since the beginning of ocean navigation, a number of methods have been brought in for making the voyage through long and vast seas easier. Several of traditional practices, using geometry, astronomy and even special instruments, helped sailors to navigate to their destinations for a quite long period.
In the ancient times, long before the ship’s clock became common in use, sailors relied on time derived from the position of sun, moon, and stars- now known as Celestial navigation.
Sometimes, in addition to their know-how tools, it was just luck that protected them when they ventured out into the uncharted, dangerous waters.
In the later periods, the mariners succeeded in developing charts depicting distant shorelines and common features of the sea during voyages. According to historical records, such charts developed in the earlier period were marked with simple outlines of coastlines made to support written or oral directions.
In addition to these, compasses, astrolabes, and callipers were the tools that were in use by ocean navigators in the earlier times. The Mariner’s Compass, which was one of the earliest navigational tools and an early form of the magnetic compass, had been used widely in the earlier periods.
Primarily, this compass was used to determine the direction of the wind when the sun was not visible. Similarly, the cross-staff, astrolabe, and quadrant were in use to help sailors determine latitude in several stages of maritime navigation.
